The present invention relates to a non-invasive method and to an apparatus for detecting biological activities in a bodily fluid specimen sample, such as blood or sputum. Specimen samples and a culture medium are introduced into sealable containers, such as vials, and are then exposed to conditions enabling a variety of metabolic, physical, and chemical changes to take place in time presence of microorganisms within the sample.
The presence of a biologically active agent, such as bacteria in a patient's body fluids, especially blood, is generally determined using culture vials. A small quantity of the bodily fluid is injected through an enclosing rubber septum into a sterile vial containing a culture medium. The vial is incubated at 37.degree. C. and monitored for microorganism growth.
A technique used to detect the presence of microorganisms involves visual inspection. Generally, visual inspection involves monitoring the turbidity or eventual color changes of tile liquid suspension of a bodily fluid and culture medium. Known sensors respond to changes in pH, oxygen concentration, or carbon dioxide concentration by changing their reflectivity, opacity, color or by changing their fluorescence intensity. The outputs from these sensors are generally based upon light intensity measurements. Light sources used to excite the sensors or the photodetectors used to monitor intensities exhibit aging effects over time. This means that errors may occur. Additionally, vial positioning is extremely important when intensity measurements are required. Even minor vial mis-positioning may affect detection measurements. Further, it is not always possible to make incubators completely light tight. Random light entering an incubator may cause dark currents, also affecting detection measurements.
Disadvantages of intensity-based methods may be overcome by using modulated excitation light in combination with sensors that change their fluorescence decay time in response to changing pH, oxygen concentration, carbon dioxide concentration, or in response to other biological activities. Using this approach, intensity measurements are replaced with time measurements, so intensity changes do not influence the results. However, fluorescence decay time sensors require high-brightness short-wavelength light sources (550 nm or shorter) that are intensity-modulated at very high frequencies (typically above 100 MHz). Because such a light source/modulator combination is expensive, vials would have to be moved to the light source instead of having a light source for each vial. Moving parts, and the relatively long time interval between successive measurements for each vial are additional concerns. Nor is it likely that inexpensive high-brightness short-wavelength semiconductor diode lasers will be developed soon.
In known automated non-invasive culture systems, individual light sources, spectral excitation/emission filters, and photodetectors are arranged by each vial. This results in station sensitivity variations from one vial to the next. Therefore, extensive and time-consuming calibration procedures are required to operate such systems. In addition, flexible electrical cables are required to connect the individual sources and detectors with the rest of the instrument. With the large number of light sources, typically 240 or more per instrument, maintenance can become very cumbersome and expensive when individual light sources start to fail.
The method and apparatus of the present invention solves the inherent problems of the prior art, using a single high energy light source in conjunction with a light beam deflector, to detect biological activity in a large number of vials. Manufacturability and the ability to detect biological activity are increased while cost is lowered.